Modern technology and an enlarging human population have combined to produce an ever increasing volume of waste material. Much of this material is composed of organic or carbonaceous substances which do not decompose quickly by natural processes. The growing accumulation of waste materials has created extremely serious problems.
Existing landfill or dump sites are rapidly filling. Creation of new dump sites requires additional land that should preferably be put to other uses or be preserved in its natural state. Environmental concerns create further complications. Dump sites and wastes processing operations can be a major source of air and water pollution. Some wastes are toxic or infectious and thus cannot be disposed of in the same manner as other garbage.
Cost considerations have prevented update and expansion of sewage treating facilities to meet the needs of the growing populations of many communities. This has created serious health hazards in many areas.
Some waste materials can be burned but this releases pollutants into the atmosphere regardless of how carefully the incinerator products are scrubbed before being released.
Certain organic materials can be decomposed and be converted to useful synthesis gases by known gasification processes. For instance, when coal is heated out of contact with air it is resolved into the stable solid residue known as coke and a volatile matter, the principal constituent of which is coal gas. The coke residue may be gasified in steam to make water gas. Coal gas and mixtures of coal gas and water gas have been used extensively as a public or industrial fuel. A lower order gas, known as producer gas, can be made by blowing air or a mixture of air and steam through a deep hot bed of coal.
Gasification of organic materials by the above described known processes produces and releases pollutants. Many such processes also produce tars and other undesirable volatiles that degrade the quality of the synthesis gas and also foul the equipment that is used to produce the gas. The processes oxidize a considerable amount of the carbon in the feedstock into carbon dioxide which is not combustible and which therefore lowers the energy content of the synthesis gas.
Synthesis gas produced by the prior processes can be converted to methanol, a combustible liquid fuel, by known techniques. Methanol produced by the prior processes tends to be contaminated with water owing to impurities in the gas.
It has previously been recognized that a variety of organic waste materials can be decomposed without pollutant production and that a fuel gas of higher energy content can be produced by performing a gasification process in a high temperature, chemically reducing atmosphere. The reactor chamber is sealed to exclude air and thus free oxygen from the reaction and superheated steam is injected into the chamber. Chemical elements in such an atmosphere are reduced to a lower oxidation state as opposed to the oxidizing processes which occur in earlier forms of gasifier. Organic compounds in the feedstock, including toxic substances, are decomposed and the products of the reaction are a very high quality synthesis gas and a residue of inorganic salts.
Prior waste gasifiers which operate with a reducing atmosphere have characteristics which variously limit throughput or result in undesirably high operating costs. Some require refluxing or repeated passages of the waste material through a high temperature zone in order to fully decompose the material. Others require a high input of electrical energy from an external source for the purpose of operating electrical heaters. Some are not readily adaptable to the processing of a variety of different waste materials. The prior waste gasifiers require large amounts of water for the boilers which supply steam to the reaction chamber. This would produce an excessive amount of boiler scale in a high volume waste processor and, as a practical matter, it would be necessary to provide costly distilled or deionized water to such a waste processor using the prior technology.
The present invention is directed to overcoming one or more of the problems discussed above.